散射技术在多酸溶液研究中的应用
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摘要
多金属氧酸盐(即多酸)是一大类主要由金属-氧多面体连接构成、结构明确、大小在纳米级(尺寸从1～10nm)的分子簇.多酸因为其丰富的组成与结构,在催化、光电材料、单分子磁体、质子导体、磁性材料、生物材料等领域有着非常广泛的应用.但是如何设计与合成具有特定结构和功能的多酸分子簇,是多酸化学家面临的一个难题,需要对多酸的溶液行为进行深入的研究.随着表征技术的发展,人们利用各种信号源,例如,微波、(近)红外、可见光、紫外光、X射线和中子,发展而来的散射技术在研究材料的结构和动力学方面有着非常重要的应用.本文同时介绍了激光光散射技术(LLS)、小角X射线散射技术(SAXS)和小角中子散射技术(SANS)在多酸溶液研究中的应用,为研究多酸在溶液中的自组装行为、自识别行为、形貌结构、形成机理、反离子分布、分子间相互作用、受限小分子动态行为等提供强有力的技术支持.这些多酸结构与动态行为相关方向的探索对于发展新型多酸的合成方法以及优化多酸的功能具有重要的指导意义.
Polyoxometalates(POMs), a large group of well-defined nanoclusters, are formed by linking early-transition-metal oxide polyhedrons through shared corners, edges and planes. POMs are widely used in various fields, such as catalysis, single molecular magnets, photoelectric materials, proton conductors, magnetic materials, and biomaterials, due to their abundant compositions and structures. However, how to design and synthesize POMs with specific structure and function remains a challenge for researchers. In-depth studies of POMs' solution behavior are required to solve this problem. Scattering techniques, using microwaves,(near)infrared, visible light, ultraviolet light, X-rays, and neutrons as probe, are employed to investigate the structure and dynamics of materials. By detecting the interactions between the probe and the particles, physical properties, such as particle size, shape and internal structure, can be determined. This article focuses on the application of laser light scattering(LLS), small angle X-ray scattering(SAXS), and small angle neutron scattering(SANS) in the study of polyoxometalate solutions. By LLS, researchers discovered the self-assembly of POM macroanions, for example, researchers find the supramolecular blackberry structure formed by {Mo_(154)} macroions in aqueous solution. Meanwhile the self-assembly processes and the self-recognition behaviors were determined, in mixed dilute aqueous solutions, the clusters {Mo_(72)Fe_(30)} and {Mo_(72)Cr_(30)} self-assemble into different "blackberry" structures of the Cr_(30) and Fe_(30) type. SAXS are employed to study POMs' morphology and solution behavior, determine the counterion distribution around POMs in solutions, and probe the interactions among POMs in solutions. The effect of Rb+ on the assembly process, and the effect of solvent polarity on the assembly process, all of these can determined by SAXS. Moreover, the kinetic behaviors of confined hydrogen atoms in POMs and the morphology of POMs in hybrid materials can be obtained through SANS. Researchers study the difference between the mean square displacement measured in fully hydrogenated and partially deuterated {Mo_(72)V_(30)} by SANS. These studies are instructive to the design of POMs' structure and function. However, there are still many basic problems of POM need to be solved. For example, the correlation between structure and properties of POM. And in the preparation of POM, how do the reducing agent, pH and catalyst work? Solving these basic issues requires numerous chemists' effort. Scattering techniques play a key role in the study of polyoxometalate solutions since the structure and morphology information of nanoscale molecules can be obtained. With its unique advantages, scattering techniques will promote the development of POM.
Polyoxometalates(POMs), a large group of well-defined nanoclusters, are formed by linking early-transition-metal oxide polyhedrons through shared corners, edges and planes. POMs are widely used in various fields, such as catalysis, single molecular magnets, photoelectric materials, proton conductors, magnetic materials, and biomaterials, due to their abundant compositions and structures. However, how to design and synthesize POMs with specific structure and function remains a challenge for researchers. In-depth studies of POMs' solution behavior are required to solve this problem. Scattering techniques, using microwaves,(near)infrared, visible light, ultraviolet light, X-rays, and neutrons as probe, are employed to investigate the structure and dynamics of materials. By detecting the interactions between the probe and the particles, physical properties, such as particle size, shape and internal structure, can be determined. This article focuses on the application of laser light scattering(LLS), small angle X-ray scattering(SAXS), and small angle neutron scattering(SANS) in the study of polyoxometalate solutions. By LLS, researchers discovered the self-assembly of POM macroanions, for example, researchers find the supramolecular blackberry structure formed by {Mo_(154)} macroions in aqueous solution. Meanwhile the self-assembly processes and the self-recognition behaviors were determined, in mixed dilute aqueous solutions, the clusters {Mo_(72)Fe_(30)} and {Mo_(72)Cr_(30)} self-assemble into different "blackberry" structures of the Cr_(30) and Fe_(30) type. SAXS are employed to study POMs' morphology and solution behavior, determine the counterion distribution around POMs in solutions, and probe the interactions among POMs in solutions. The effect of Rb+ on the assembly process, and the effect of solvent polarity on the assembly process, all of these can determined by SAXS. Moreover, the kinetic behaviors of confined hydrogen atoms in POMs and the morphology of POMs in hybrid materials can be obtained through SANS. Researchers study the difference between the mean square displacement measured in fully hydrogenated and partially deuterated {Mo_(72)V_(30)} by SANS. These studies are instructive to the design of POMs' structure and function. However, there are still many basic problems of POM need to be solved. For example, the correlation between structure and properties of POM. And in the preparation of POM, how do the reducing agent, pH and catalyst work? Solving these basic issues requires numerous chemists' effort. Scattering techniques play a key role in the study of polyoxometalate solutions since the structure and morphology information of nanoscale molecules can be obtained. With its unique advantages, scattering techniques will promote the development of POM.
引文
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23 Haso F,Yang P,Gao Y,et al.Exploring the effect of surface functionality on theself-assembly of polyoxopalladate macroions.Chem Eur J,2015,21:9048-9052
24 Kistler M L,Bhatt A,Liu G,et al.A complete macroion-“blackberry”assembly-macroion transition with continuously adjustable assembly sizes in{Mo132}water/acetone systems.J Am Chem Soc,2007,129:6453-6460
25 Nakamura I,Miras H N,Fujiwara A,et al.Investigating the formation of“molybdenum blues”with gel electrophoresis and mass spectrometry.J Am Chem Soc,2015,137:6524-6530
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